Quanqin Dai

Jilin University, Jilin, Jilin Sheng, China

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Publications (33)107.68 Total impact

  • Current Nanoscience 12/2012; 8(6):909-913. · 1.36 Impact Factor
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    ABSTRACT: The metastable wurtzite nanocrystals of CuGaS(2) have been synthesized through a facile and effective one-pot solvothermal approach. Through the Rietveld refinement on experimental X-ray diffraction patterns, we have unambiguously determined the structural parameters and the disordered nature of this wurtzite phase. The metastability of wurtzite structure with respect to the stable chalcopyrite structure was testified by a precise theoretical total energy calculation. Subsequent high-pressure experiments were performed to establish the isothermal phase stability of this wurtzite phase in the pressure range of 0-15.9 GPa, above which another disordered rock salt phase crystallized and remained stable up to 30.3 GPa, the highest pressure studied. Upon release of pressure, the sample was irreversible and intriguingly converted into the energetically more favorable and ordered chalcopyrite structure as revealed by the synchrotron X-ray diffraction and the high-resolution transmission electron microscopic measurements. The observed phase transitions were rationalized by first-principles calculations. The current research surely establishes a novel phase transition sequence of disorder → disorder → order, where pressure has played a significant role in effectively tuning stabilities of these different phases.
    Nanoscale 10/2012; · 6.73 Impact Factor
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    ABSTRACT: In the present work, we demonstrated a simple and green synthesis route for shape-controlled ZnS nanocrystals, where only environmentally benign chemicals, namely sulfur, zinc oxide and olive oil, were employed. By controlling the experimental conditions, we were able to tune the band edge and trap state photoluminescences of ZnS nanocrystals and obtain pure excitonic photoluminescence that was rarely observed in literature. The trap state emission was derived from sulfur vacancies and would be eliminated when an excess of sulfur was used during the synthesis. Additionally, the morphology of ZnS nanocrystals could be tuned to appear like flowers, where the formation mechanism was systematically discussed.
    Journal of hazardous materials 11/2011; 211-212:62-7. · 4.33 Impact Factor
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    ABSTRACT: A small quantity of tributylphosphine was employed to improve the surface state of fresh and oxidized PbSe nanocrystals after the formation of nanocrystals. Experimental results showed that the photoluminescence intensity increased in both situations. However, an excessive amount of tributylphosphine exhibited negative effects of decreasing photoluminescence and particle aggregation. A suitable amount of tributylphosphine added before the synthesis of a CdSe shell on PbSe core (PbSe/CdSe) also exhibited a photoluminescence intensity increase for these core/shell nanocrystals. KeywordsSemiconductor nanocrystals–PbSe–PbSe/CdSe–Core/shell–Tributylphosphine
    Journal of Nanoparticle Research 09/2011; 13(9):3721-3729. · 2.18 Impact Factor
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    ABSTRACT: Multiple CdSe and ZnSe semiconductor shells were grown on PbSe semiconductor spherical cores with monolayer control. For CdSe shell coating, we found that there was little room to further increase the quantum yields of freshly-made high-quality PbSe nanocrystals that already owned very high initial values because of their good surface status; but there was great improvement for the PbSe nanocrystals with low initial quantum yields because of the poor surface status. Nonetheless, the quantum yield for the latter case could not reach the former's value. Additional ZnSe shells on PbSe/CdSe could further increase the quantum yield and protect the nanocrystals from air oxidation. The observed phenomena in the synthesis of the PbSe/CdSe and PbSe/CdSe/ZnSe core/shell structures were explained through the carrier wave function expansion and the surface polarization.
    Langmuir 06/2011; 27(15):9583-7. · 4.38 Impact Factor
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    ABSTRACT: Colloidal IV–VI SnSenanocrystals with small and uniform size distribution were synthesized by a facile and phosphine-free method. Simple Sn6O4(OH)4 was introduced as a tin precursor to synthesize the SnSenanocrystals. By changing the reaction temperature and Sn/Se molar ratio, SnSenanocrystals with different shapes and sizes were achieved. The influence of reaction temperature and Sn/Se molar ratio to the shape and size of SnSenanocrystals has been discussed detail. Similar to other IV–VI tin chalcogenides, SnSe shows potential as energy storage material. The performance of SnSenanocrystals as an anode material for lithium ion batteries has been investigated. A mechanism for SnSe as anode material has been proposed based on its performance. The influence of the shape and size of the SnSenanocrystals on the performance of lithium ion batteries has been discussed in detail.
    CrystEngComm 05/2011; 13(12):4161-4166. · 3.88 Impact Factor
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    ABSTRACT: In comparison to the previous lengthy approaches, we described a general and simple strategy for engineering the superlattice assembly of IV-VI semiconductor nanocrystals (NCs) with tunable sizes and morphologies. Not only the well-studied spherical NCs but also some special-shaped NCs, such as the quasi-cubic, cubic, truncated octahedral, and octahedral, could self-assemble into well-ordered patterns, as demonstrated in PbS, PbSe, and PbTe. These results extended our proposed model about the configuration of ligand chains in the superlattice assembly. This powerful capability of assembling superlattices was dominated by a heat-treatment process, providing a significant and extensive direction in the engineering of morphology-tunable NC superlattices.
    Langmuir 12/2010; 26(24):19129-35. · 4.38 Impact Factor
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    ABSTRACT: This paper reports the effect of ligands including oleic acid (OA), trioctylphosphine (TOP), and tributylphosphine (TBP) on the PbSe nanocrystal growth during synthesis, as well as the effect of OA ligands on the nanocrystal stability after synthesis. These ligands play important roles in the nucleation and growth mechanism of nanocrystals. We have discovered that the ligand effect on the growth of PbSe nanocrystals can differ from that on the mostly studied CdSe nanocrystals. Also, we present a method for producing relatively smaller and more monodisperse PbSe nanocrystals based on our new understanding that the use of TBP, instead of the generally reported TOP, can slow down the growth of PbSe nanocrystals. In addition, our postsynthetic investigation of OA ligand effects demonstrate the dominant desorption of OA-bonded Pb atoms, causing the shrinkage of PbSe nanocrystals. This provides some insight into stabilization strategies for labile PbSe nanocrystals.
    The Journal of Physical Chemistry C 09/2010; 114(39). · 4.84 Impact Factor
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    ABSTRACT: SnS nanocrystals have been synthesized in a simple and facile way. Sn(6)O(4)(OH)(4) is introduced to synthesize tin sulfide, which is used as tin precursor. By changing the reaction conditions (reaction temperature and Sn/S molar ratio), SnS nanocrystals with different shape and size can be produced. SnS nanoparticles and nanoflowers with orthorhombic crystal structure have uniform size distribution. The SnS nanoflowers firstly transform to polycrystalline nanoflowers, and then become amorphous nanosheets. The drive force of amorphization reduces the high free-energy of nanocrystals. The layered crystal structure of SnS is the main reason for the shape evolution and amorphization processes. The optical properties of nanoparticles are investigated by optical absorption spectra. The optical direct band gap and optical indirect band gap in SnS nanoparticles are 3.6 eV and 1.6 eV, respectively. Compared to direct band gap (1.3 eV) and indirect band gap (1.09 eV) in bulk SnS, both direct transition and indirect transition in nanoparticles show an obvious quantum-size effect.
    Nanoscale 09/2010; 2(9):1699-703. · 6.73 Impact Factor
  • Source
    Quanqin Dai, Chad E Duty, Michael Z Hu
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    ABSTRACT: In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white light-emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.
    Small 08/2010; 6(15):1577-88. · 7.82 Impact Factor
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    ABSTRACT: An investigation show that the temperature-induced band gap (E(g)) variation of PbSe nanocrystals is strongly size-dependent. The temperature coefficients (dE(g)/dT) evolve from negative to zero and then to positive values, with the increase of PbSe nanocrystal sizes. Such phenomena imply that PbSe nanocrystals may be the potential candidate as sensitive temperature markers. Additional analyses disclose that the molar extinction coefficients of PbSe nanocrystals remain unchanged in the investigated temperature range (25-120 degrees C).
    Langmuir 07/2010; 26(13):11435-40. · 4.38 Impact Factor
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    ABSTRACT: We presented a facile and efficient route to prepare single-component nanoparticle (NP) superlattices. It was demonstrated that mutual transformation between random NPs and their well-ordered superlattices could be unified by a proposed model of ligand configuration. When the ligand chains capped on NPs were disordered at room temperature, NPs existed separately in solution, which were noninteracting and thus showed random states on transmission electron microscopy (TEM) grids; comparatively, the ligand chains capped on NPs in an ordered state in solution would correspond to superlattice structures obtained on TEM grids. These experimental observations were consistent with our theoretical analysis.
    Journal of Physical Chemistry C - J PHYS CHEM C. 06/2010; 114(26).
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    ABSTRACT: A liquid-core fiber has been experimentally investigated by inserting PbSe/toluene solution media in the hollow-core of a capillary waveguide. Upon pumping by a 532 nm-CW laser, a good amplified stimulated emission in 1290 nm band was obtained.
    01/2010;
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    ABSTRACT: SnTenanocrystals with different shapes and sizes are synthesized by a simple and facile method. The length of the fatty chain in amine has an important effect on the shape and size of SnTenanocrystals. When oleylamine (OLA) is used as ligand, SnTenanoparticles with size of 4 nm and high crystallinity are produced. However, when octylamine (OTA) is used as ligand, larger SnTenanoparticles with low crystallinity are achieved, which would transform into single crystal SnTenanowires with increasing reaction time. The driving force of shape evolution of SnTenanocrystals is reducing the high surface free energy. An oriented attachment mechanism is proposed to explain the transition from nanoparticles to nanowires, and oriented attachment of nanoparticles to single crystal nanowires is proposed to reduce the interface energy by the greatest amount.
    CrystEngComm 01/2010; · 3.88 Impact Factor
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    ABSTRACT: PbSe/CdSe core/shell nanocrystals with quantum yield of 70% were obtained by the "successive ion layer adsorption and reaction" technology in solution. The thickness of the CdSe shell was exactly controlled. A series of spectral red shifts with the CdSe shell growth were observed, which was attributed to the combined effect of the surface polarization and the expansion of carriers' wavefunctions. The stability of PbSe nanocrystals was tremendously improved with CdSe shells.
    Nanoscale Research Letters 01/2010; 5(8):1279-83. · 2.52 Impact Factor
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    ABSTRACT: SnO nanoplates, nanosheets and nanorings have been synthesized by a simple and facile approach. By changing the reaction temperature, SnO nanoplates would become to individual SnO nanosheets. Complex nanostructures disassemble to its basic unit. When reaction temperature is much higher, novel SnO nanorings by assemble of nanosheets appear. Assemble processes and disassemble processes are observed in this experiment. Ligand plays a key role in the morphology evolution of nanocrystals. The ligand interaction mechanism is proposed to explain the transition from nanoplates to nanosheets, and ligand protection mechanism is used to explain the formation of nanorings. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM) images, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Fourier transform infrared spectrometry (FTIR) are used to characterize these samples.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2010; 363:30-34. · 2.11 Impact Factor
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    ABSTRACT: In this work, we presented a facile approach for the preparation of three-dimensional PbS nanoflowers, which was attributed to the coexistence of two types of amines with different-length alkyl chains and different steric hindrance. These monodisperse PbS nanoflowers showed small particle sizes (35 nm) and narrow size distribution (dz9%). On the basis of these nanoflowers, we obtained a series of singlecrystal hollow PbS nanostructures with tunable morphologies (including sphere, cuboctahedron, cube, and tube/rod) through elevating reaction temperature and prolonging growth time. It was further followed by a detailed discussion of the mechanism of morphology evolution, where the recrystallization and intraparticle ripening made contributions.
    CrystEngComm 01/2010; · 3.88 Impact Factor
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    ABSTRACT: Infrared-emitting PbSe nanocrystals are of increasing interest in both fundamental research and technical application. However, the practical applications are greatly limited by the poor stability of PbSe nanocrystals. We firstly investigated the stability of PbSe nanocrystals under different conditions. Absorption and photoluminescence spectra of PbSe nanocrystals were utilized to observe material stability for some conventional factors, i.e. particle concentration, particle size, temperature, light exposure, contacting atmosphere, and storage forms (solution or solid powder). Both absorption and luminescence spectra of PbSe nanocrystals were affected by particle size, particle concentration, and light exposure, which caused large and quick blue-shifts in the optical spectra. The photoluminescence emission intensity of the PbSe nanocrystal solution under ultraviolet (UV) exposure in air increased first and then decreased slowly; without UV irradiation, the emission intensity monotonously decreased over time. However, if stored under nitrogen, no changes in absorption and photoluminescence spectra of the PbSe nanocrystals were observed even with UV exposure or being heated up to 100 oC. Then we determined the atomic compositions and molar extinction coefficients of PbSe semiconductor nanocrystals by atomic absorption spectrometry, UV-Vis-NIR spectrophotometry, and transmission electron microscopy. The Pb/Se atomic ratio was found to be size-dependent with a systematic excess of Pb atoms in the PbSe nanocrystal system. Experimental results indicated that the individual PbSe nanocrystal was nonstoichiometric, consisting of a PbSe core and an extra layer of Pb atoms. For these nonstoichiometric PbSe semiconductor nanocrystals, we proposed a new computational approach to calculate the total number of Pb and Se atoms in different sized particles. This calculation played a key role on the accurate determination of the strongly size-dependent extinction coefficient, which followed a power law with an exponent of ~ 2.5.
    36th American Chemical Society Northeast Regional Meeting; 10/2009
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    ABSTRACT: Hierarchical SnO nanocrystals are synthesized by a reproducible and facile way via decomposition of an intermediate product tin oxide hydroxide, Sn6O4(OH)4. By changing the amount of injecting water, layer-plate-like, nest-like, stepwise-bipyramid-like, and defective stepwise-bipyramid-like hierarchical SnO nanocrystals could be obtained. All of these hierarchical SnO nanostructures are constructed by smaller nanosheets. The driving force of aggregation is reducing the surface energy of nanocrystals. Water played a key role in the control morphologies of hierarchical SnO nanostructures. The water control decomposition (WCD) mechanism was proposed to explain the effect of water on the morphologies. On the basis of reaction kinetics, the different superfluous injected water after reaction would restrain the decomposition of Sn6O4(OH)4 to SnO nanosheets; a different amount of superfluous injected water would induce a different reaction rate. At different reaction rates, SnO nanosheets would have different sizes and different approaches to aggregation, and different hierarchical SnO nanocrystals appeared by injecting different amounts of water into the reaction. Typically, hierarchical SnO nanocrystals as an anode material for lithium ion batteries are studied. These SnO nanocrystals show good potential for lithium battery materials. Among these SnO nanostructures, the stepwise-bipyramid-like nanostructure shows the best properties.
    Journal of Physical Chemistry C - J PHYS CHEM C. 08/2009; 113(32).
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    ABSTRACT: Infrared-emitting PbSe nanocrystals are of increasing interest in both fundamental research and technical application. However, the practical applications are greatly limited by their poor stability. In this work, absorption and photoluminescence spectra of PbSe nanocrystals were utilized to observe the stability of PbSe nanocrystals over several conventional factors, that is, particle concentration, particle size, temperature, light exposure, contacting atmosphere, and storage forms (solution or solid powder). Both absorption and luminescence spectra of PbSe nanocrystals exposed to air showed dependence on particle concentration, size, and light exposure, which caused large and quick blue-shifts in the optical spectra. This air-contacted instability arising from the destructive oxidation and subsequent collision-induced decomposition was kinetically dominated and differed from the traditional thought that smaller particles with lower concentrations shrank fast. The photoluminescence emission intensity of the PbSe nanocrystal solution under ultraviolet (UV) exposure in air increased first and then decreased slowly; without UV irradiation, the emission intensity monotonously decreased over time. However, if stored under nitrogen, no obvious changes in absorption and photoluminescence spectra of the PbSe nanocrystals were observed even under UV exposure or upon being heated up to 100 degrees C.
    Langmuir 07/2009; 25(20):12320-4. · 4.38 Impact Factor

Publication Stats

140 Citations
107.68 Total Impact Points

Institutions

  • 2006–2012
    • Jilin University
      • • State Key Lab of Superhard Materials
      • • College of Electronic Science and Engineering
      • • Department of Material Science and Engineering
      Jilin, Jilin Sheng, China
    • Changchun Institute of Optics, Fine Mechanics and Physics
      Hsin-ching, Jilin Sheng, China
  • 2009–2011
    • Worcester Polytechnic Institute
      • Department of Chemistry and Biochemistry
      Worcester, MA, United States
  • 2010
    • Oak Ridge National Laboratory
      Oak Ridge, Florida, United States